Programmed digital to analog function generator for a motor controlled x-y plotter



May 28,1968

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R \3 Qt o m N SH W4 0 N A f, P 6 Q N\u R MQN Q O NR May 28, 1968 P BRQCK ET AL PROGRAMMED DIGITAL TO ANALOG FUNCTION GENERATOR FOR A MOTOR CONTROLLED X-Y PLOTTER Original Filed DeC. 29, 1961 19 Sheets-Sheet l9 United States Patent PROGRAMMED DIGITAL TO ANALOG FUNCTION GENERATOR FOR A MOTOR CONTROLLED X-Y PLOTTER Paul Brock and Peter J. Foy, Encino, Calif., assignors to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Continuation of application Ser. No. 163,263, Dec. 29, 1961. This application Aug. 2, 1965, Ser. No. 477,668

3 Claims. (Cl. 318-162) This application is a continuation of application Ser. No. 163,263, filed Dec. 29, 1961, entitled, Electrical Systern.

This invention relates generally to systems of electrical control, and more particularly to such systems which are capable of accurately positioning and moving an element in accordance with a predetermined instruction program.

While the descriptive disclosure hereinafter is particularly directed to a system for moving a pen or other line drawing implement according to a specified program for the purpose of making drawings, writing, printing and the like, it will be appreciated that this invention is not particularly limited to such a specific function or to such a particular type of output device but may be used to power any suitable device in the layout or manufacture of printed circuits in machining operations, etc.

Efforts have been made by others to automatize drafting, that is, to automatize the making of line drawings. These prior art systems have been developed to the point where the specific drawing is completely encoded on a digital record member as a digital program. These systems are usually based upon a system of mathematics, defining straight lines in point-slope form. The digital program is transduced in a specific sequence and converted to analog form to power a suitable type of analog servo system having a pair of servo motors which power and move a single output member in each of two mutually perpendicular directions.

These prior art arrangements have proved satisfactory for drawing straight lines at differing slopes. They have, however, been particularly limited to the drawing of straight lines. In such systems curves have been simulated by drawing short, straight lines of progressively changing slopes in end-to-end relationship. In a system of this type, depending upon how accurately a curved line is to be simulated, the use of shorter and shorter straight line segments requires correspondingly larger numbers of definitions of line start and end points to achieve the desired approximated curve. This is a very time consuming operation from the viewpoint of preparing the program, as well as from the viewpoint of the time of operation of the machine in reading and reproducing these multitudes of short, straight line segments in simulating curves.

An object of this invention is to provide an improved system for selectively generating both straight lines and curves.

A further object of this invention is to provide an improved system for generating geometric figures in which the position of the figure in a reference plane, such as a drawing board, is defined in terms of rectangular coordinates from a fixed point of reference to the geometric center of the figure.

It is also an object of this invention to provide an improved system for generating geometric figures in which the geometric figures are defined in two coordinates with respect to their geometric centers.

More particularly it is an object hereof to provide an improved system for generating geometric figures in which provision is made for completely defining a geometric figure in a reference plane in terms of distances in two coordinates from a reference point in the reference plane 3,386,020 Patented May 28, 1968 to the geometric center of the figure, together with distances in two coordinates difining the figure with respect to its geometric center.

It is additionally an object of this invention to provide an improved electrical control system including provisions for generating a plurality of time varying electrical quantitles and steady state electrical quantities and for combining these differing quantities in differing ways to produce an electrical quantity having a desired time varying characteristic.

The aforesaid and other objects and advantages are achieved in an arrangement according to this invention which generates and employs time variable electrical quantities characterized by selected time parametric functions for controlling a servo system to selectively describe straight lines, circular arcs, or circles, and elliptical arcs, or ellipses, of specific dimension or sizes and at particularly defined points in a given reference plane, such as a drawing board.

The program of the servo system is digitally encoded on a suitable record medium, such as paper tape, magnetic tape or other record bearing medium, as a discrete information code system in conventional binary code, for instance, together with other discrete information recordings having place of position significance on the medium for directing control of specific control elements in the system. Suitable transducers read this medium or tape and the signals thus generated after suitable conversion, amplification and shaping, if needed, are stored in a digital storage circuit such as a shift register which may include a plurality of fiip flops conventionally set in correspondence with the respective discrete signals. The digitally encoded information includes the following:

(1) Dimensions in both coordinates from a reference point in the reference plane to the geometric center of the figure which is to be drawn.

(2) Dimensions and their signs defining the starting point of any line describing a geometric figure in terms of the respective coordinates of that point referred to the geometric center of the figure.

(3) Dimensions and their signs defining the stopping point of any line.

(4) Respective commands denoting if a circular are or an ellipse is to be drawn.

(5) Respective commands denoting which of several line thicknesses is to be used.

(6) Respective commands denoting if any of several line interruption patterns (line characteristics) is to be used.

The system includes a variable frequency electrical function generator for generating sine and cosine electrical quantities of a fixed magnitude which are relatively positive or negative depending upon the algebraic signs of the coordinates defining the starting point of the line describing the geometric figure in relation to the geometric center of the figure and which vary in frequency as a function of a selected algebraic combination of at least a portion of the information defining these coordinates to provide time varying output voltages having a frequency roughly inversely proportional to the desired length of a line.

The time varying voltages thus generated are attenuated, Or amplitude modulated, or multiplied by another voltage, or otherwise suitably modified, in selected pairs as a function of the coordinates of the starting point of the line defining the figure to provide simultaneous time varying X and Y line generating voltages, the corresponding instantaneous magnitudes of which jointly define respective points on the line describing the figure.

Respective position servos, termed the X and Y servos herein, are connected to and power a single output element such as a pen, for instance. The time varying volt- 

1. AN ELECTRICAL SYSTEM OF CONTROL, COMPRISING: A PAIR OF MOTORS; A DEVICE HAVING A PAIR OF INPUT MEMBERS CONNECTED TO SAID MOTORS, RESPECTIVELY, AND HAVING A MOVABLE OUTPUT MEMBER COUPLED TO AND DRIVEN BY BOTH INPUT MEMBERS; A WORK MEMBER ON SAID OUTPUT MEMBER OPERABLE BETWEEN OPERATIVE AND INOPERATIVE CONDITIONS; AN OSCILLATOR HAVING AN OUTPUT CIRCUIT FOR PRODUCING A FIXED AMPLITUDE SINE VOLTAGE; FIRST CIRCUIT MEANS INCLUDING AN AMPLITUDE MODULATOR COUPLING SAID OUTPUT CIRCUIT OF SAID OSCILLATOR TO ONE OF SAID MOTORS; SECOND CIRCUIT MEANS INCLUDING AN AMPLITUDE MODULATOR COUPLING SAID OUTPUT CIRCUIT OF SAID OSCILLATOR TO THE OTHER OF SAID MOTORS; CIRCUIT MEANS COUPLED TO SAID OSCILLATOR AND SAID WORK MEMBER FOR STARTING SAID OSCILLATOR AND RENDERING SAID WORK MEMBER OPERATIVE; AND A STOP SIGNAL CIRCUIT SYNCHRONIZED WITH SAID OSCILLATOR AND COUPLED TO SAID WORK MEMBER FOR RENDERING SAID WORK MEMBER INOPERATIVE. 